David Williams is Mr. Pumblechook. He's an author too.

I just posted one of the first pictures from the Great Expectations set and learned a couple of fun things about David Williams who plays Pumblechook. Besides being best known for his work on Little Britain he's also an author of hilarious childrens' books. His debut children's novel, The Boy in the Dress, was published in 2008 to unanimous critical acclaim and shortlisted for the Roald Dahl Funny Prize. His second book, Mr Stink, was one of Amanda Craig’s Children’s Books of the Year in the London Times. His most recent book, Gangsta Granny was just published this past November. For the time being I don't think you can buy his books in the United States but you can go to the Amazon's UK site.